Frangible molds



Aug. 18, 1970 J. COLLMAN ET AL 3,524,618

FRANGIBLE MOLDS' Filed July 17, 1967 INVENTORS JOEL COLLMAN LOWELL R. ALVORD HOWARD E. TUCKER AGENT United States Patent 3,524,618 FRANGIBLE MOLDS Joel Collman, Roy, and Lowell R. Alvord, Ogden, Utah,

and Howard Tucker, Malad, Idaho, assignors to Thinkol Chemical Corporation, Bristol, Pa., a corporation of Delaware Filed July 17, 1967, Ser. No. 653,690 Int. Cl. B28b 7/34 US. Cl. 249-61 3 Claims ABSTRACT OF THE DISCLOSURE A frangible mold having a tape interwoven around frangible studs encased in a frangible matrix. The mold is fragmented by pulling the tape.

This invention relates to molds and more particularly to molds which can be removed readily from a casting.

Solid propellant rocket grains are presently being cast around molds to form internal configurations, such as slots, in the grain. Often the internal configuration is complex and located so that it is difficult to remove the mold from the cast grain. In the prior art the problems associated with removing the mold have been dealt with in various ways, including the use of collapsible mandrels, forming the grain in segments, and removal of the mold by physically disintegrating it after the grain has been cast. In the case of the latter approach to the problem, there has been a need for a mold which can be fabricated economically and which will reliably fragment into small pieces. In accordance with the present invention, a mold is provided having a relatively thin member formed with a plurality of studs projecting from one side. A continuous tape is interwoven on these studs and a matrix of foamed plastic is molded over the studs and tape. After use, the mold is disintegrated by ripping out the tape.

Accordingly, an object of this invention is to provide inexpensive means for forming slots in solid rocket propellant grains.

Another object is to provide a slot forming mold that can be easily removed from a propellant grain.

In the following description of the invention reference is made to the accompanying drawings wherein:

FIG. 1 is a perspective view of one component of a preferred embodiment of the invention;

FIG. 2 is a perspective view of the same component after a tape has been interwoven on its projecting studs;

FIG. 3 is a perspective view of a completed mold; and

FIG. 4 is a fragmentary view of a rocket propellant grain wherein a plurality of frangible molds have been used to form a slot in the grain.

Throughout the specification and the drawings, like reference numbers designate like parts.

In FIG. 1 the number generally designates a frangible sheet having a plurality of frangible studs 12 3,524,618 Patented Aug. 18, 1970 "ice projecting from one side thereof. FIG. 2 illustrates sheet 10 after a tape 14 has been interwoven around studs 12. Tape 14 is secured to stud 12', wrapped around stud 12", then about 12", and so on until the end of the respective two rows of studs is reached, after which the process is repeated on successive pairs of rows. A short length of tape 14 extends beyond the last stud, forming a free end 16.

When tape 14 is in place, plastic foam 18 is poured on the subassembly illustrated in FIG. 2. After curing, the completed mold 20 has the shape shown in FIG. 3. It will be noted that free end '16 of tape 14 extends from the narrow end of the mold.

As illustrated in FIG. 4, molds made in accordance with this invention are used to form radially extending slots in solid propellant rocket grains. A number of molds 20 are spaced in edge-to-edge relationship about the central perforation 22 of the propellant grain 24. After the propellant has been cured, molds 20 are removed by pulling the free ends 16 of the tapes embedded in the molds, thereby fragmenting the molds into small pieces readily removed from the slot.

In a preferred embodiment of the invention sheet 10 is formed of a foamed urethane plastic. Tape 14 can be made from any strong cloth, such as glass cloth or a nylon reinforced pressure sensitive adhesive tape. Foamed urethane plastic has been found particularly suitable as a matrix for encasing the tape, but other plastics can be used.

It will be understood that various changes can be made in the invention without departing from the scope of the appended claims.

What is claimed is:

1. A mold comprising:

a frangible sheet having a plurality of frangible studs projecting from one side thereof;

a tape interwoven around said studs;

a frangible matrix abutting said sheet and encasing said studs and tape, a portion of said tape extending from said matrix whereby said tape can be pulled to fragment the mold.

2. A mold as defined in claim 1 wherein said sheet,

studs and matrix are formed of a polymeric material.

3. A mold as defined in claim 2 wherein said matrix is formed of a foamed polymeric material.

References Cited UNITED STATES PATENTS 2,343,292. 3/ 1944 Greneher 249-61 2,364,710 12/ 1944 Greneher 249-61 3,136,002 6/ 1964 Schwartz 2643 SAMUEL FEINBERG, Primary Examiner US. Cl. X.R. 264-3, 221; 254 

